1. Field of the Invention
The present invention relates generally to an optical communication system, and in particular, to a cross-connect device with an electrical cross-connect switch built therein.
2. Description of the Related Art
In an optical communication system, a wavelength multiplexing is implemented to make transmission systems more economical. A cross-connect device is installed at an intermediate node between an upper node (i.e., a central base station) and a lower node (i.e., a subscriber). The cross-connect device involves transmission and assignment of channel signals. In addition, the device plays an important role in optimizing traffic, congestion, and network growth for an optical network as well as improving the network survivability.
Diverse transmission formats are available in the optical transmission system in order to transmit information at different bit rates. The common transmission formats include SDH/SONET (Synchronous Digital Hierarchy/Synchronous Optical Network), FDDI (Fiber Distributed Data Interface), ESCON (Enterprise Systems Connectivity), Fiber Channel, Gigabit Ethernet, and ATM (Asynchronous Transfer Mode), wherein each operates at 125 Mbps, 155 Mbps, 200 Mbps, 622 Mbps, 1062 Mbps, 1.25 Gbps, and 2.5 Gbps, respectively.
FIG. 1 is a block diagram of a conventional optical cross-connect device having an electrical cross-connect switch, and FIG. 2 is a block diagram of the conventional transmission optical receiver.
Referring to FIG. 1, the conventional optical cross-connect device is comprised of a demultiplexer (DEMUX) 10 for demultiplexing an input optical signal into different channels; a plurality of single transmission optical receivers 20 for converting optical channel signals received from the DEMUX 10 to electrical signals; a cross-connect switch 30 for path-routing the electrical signals received from the respective single transmission optical receivers 20; a controller 40 for controlling the path routing of the cross-connect switch 30; a plurality of single transmission optical transmitters 50 for converting the electrical signals received from each output port of the cross-connect switch 30 to optical signals; and, a multiplexer (MUX) 60 for multiplexing the optical signals received from the single transmission optical transmitters 50 onto a strand of optical fiber.
Referring to FIG. 2, each of the single transmission optical receivers 20 includes an opto-electrical converter 22 for converting an input optical signal to an electrical signal; an amplifier 24 for amplifying the electrical signal received from the opto-electrical converter 22; a clock generator 26 for generating a reference clock signal corresponding to the transmission rate of the input optical signal; and, a clock data recovery unit 28 for recovering a clock signal and data from the amplified electrical signal received from the amplifier 24.
The single transmission optical receiver 20 receives an optical signal at a predetermined transmission rate in a single transmission format applied to the corresponding optical communication system. The clock generator 26 outputs a clock signal at a predetermined single frequency, and the clock data recovery unit 28 recovers the clock signal and data by shaping the waveform of the electrical signal converted from the optical signal within the clock signal cycle.
As described above, because the conventional optical cross-connect device includes the single transmission optical receivers 20 and the single transmission optical transmitters 50 that only support one predetermined transmission format and its related transmission rate, the device is unable to operate adaptively to the change in the transmission format and the transmission rate (sometimes referred to as having no transparency). Therefore, the conventional optical cross-connect device has limitations during the operation if the transmission format used is changed, or if at least two transmission formats are employed.
To overcome the limitations, protocol-free systems have been developed to accommodate optical signals with different transmission rates. However, such protocol-free systems are confined to the waveform shaping of signals, without detecting the transmission rates of the signals and recovering clock signals. Accordingly, noise and timing jitter are produced and accumulated through the nodes which in turn deteriorate the transmission quality.
It is, therefore, an object of the present invention to provide an optical cross-connect device with transparency for accommodating optical signals with diverse transmission rates.
It is another object of the present invention to provide an optical cross-connect device with transparency for increasing transmission quality and transmission distance.
The above objects can be achieved by providing an optical cross-connect device with transparency in an optical communication system. Accordingly, the optical cross-connect device includes a demultiplexer for demultiplexing an input optical signal into different channels; a plurality of arbitrary transmission optical receivers for converting the optical channel signals received from the demultiplexer to electrical signals and for recovering a clock signal and data according to a reference clock signal generated at the transmission rate of the electrical signals; a cross-connect switch that path-routes the electrical signals received from the arbitrary transmission optical receivers; a controller for controlling the path-routing of the cross-connect switch; a plurality of arbitrary transmission optical transmitters for converting the electrical signal received from each output port of the cross-connect switch to an optical signal; and, a multiplexer for multiplexing the optical signals received from the arbitrary transmission optical transmitters onto one stand of optical fiber.